Glucocorticoids are the most effective anti-inflammatory agents presently available for the therapeutic management of inflammatory diseases such as asthma. Although one of the most notable effects of steroids is their ability to inhibit leukocyte recruitment to sites of inflammation, relatively little is known about the mechanism by which this effect occurs. The studies described in this proposal are designed to improve our understanding of the mechanisms by which steroids inhibit the recruitment and activation of leukocytes, with an emphasis on IgE-mediated inflammatory reactions. Studies are planned to analyze the molecular basis of leukocyte adherence to vascular endothelial cells focusing on eosinophils and basophils, cell types associated with IgE-mediated reactions. Potential mechanisms for selective eosinophil and basophil recruitment, involving vascular cell adhesion molecule-1 (VCAM-1) and the integrin VLA-4 have been discovered. Preliminary results have shown that interleukin-4 activates endothelial cell expression of VCAM-1 and that this response is inhibited by dexamethasone. The effects of steroids on adhesion mediated by VCAM-1 and VLA-4, as well as intercellular adhesion molecule-1 (ICAM- 1), endothelial-leukocyte adhesion molecule- 1 (ELAM- 1), Leu-8, and CD 11/18 will be analyzed with the anticipation that the results will provide insight into the mechanisms by which steroids prevent leukocyte accumulation. Recent studies suggest that exposure of eosinophils to cytokines such as granulocyte-macrophage colony-stimulating factor (GM-CSF) potentiates their functional responses (including adherence molecule expression and adherence to endothelial cells), and prolongs their survival. Since GM-CSF is observed at sites of allergen challenge in the lungs and skin, these effects are expected to increase eosinophil accumulation and activation at allergic reaction sites. Steroids have been shown to inhibit some of these responses to GM-CSF. Studies are proposed to determine the effects of steroids on eosinophil priming using a number of endpoint parameters including adherence molecule expression, adherence, leukotriene generation, intracytoplasmic calcium responses and increased survival responses. Mast cells may contribute to leukocyte recruitment by producing endothelial-activating cytokines. Whether human lung mast cells produce cytokines or cytokine mRNA following IgE-mediated activation will be determined, and the effects of steroids on any response will be assessed. Collaborative studies are proposed to test the hypothesis that steroids inhibit cytokine production and endothelial activation in vivo in human subjects using cutaneous and pulmonary challenge models as well as immunohistochemical analysis of biopsies. We anticipate that the studies described in this proposal will further our knowledge of the mechanism of the beneficial action of steroids in allergic reactions.